Sound transmitter



April 17,1928. H 1,666,262

l v H. A. MlLLs Er AL v soUND TRANSMITTER Filed Jan. 26. 1927 yf l Patented Apr. ll'l, 1928.

UNITED STATES PATENT D'FFICE.

HARRY A. MILLSAND WILLIAM D. PYLE, F DENVER, COLORADO.

SOUND TRANSMITTER.

Application led January 26, 1927. Serial No. 163,638.

' music of all kinds, together With singing by individuals and aggregations ranging all the Way from duets to choirs of a. hundred or more voices.

lt was very soon discovered that the ordinary carbon pile telephone transmitter was not adapted to Isuccessively transmit the great variety of sounds produced in'radio programs and therefore various modifications were developed and tried. There are in connnon use today two types of sound transmitters for radio broadcasting worin-one being a modification of the ordinary carbon pile transmitter and the other a transmitter in which the vibrating diaphragm forms one plate of a condenser.

The carbon transmitter, aside from being unsuitedfor transmitting the'great variety of sound vibrations is also objectionable for other reasons which need not be set out in det-ail. It is necessary, however, to call attention to the fact that When carbon transmitters are used for transmitting operas or plays, Where a large number of transmitters must be suspended about the stage, it becomes necessary to provide each transmitter With a switch and to constantly connect and disconnect the various transmitters as the singer or speaker moves about the stage.

The other type of transmitter in which the diaphragm serves as one plate of a condenser makes it necessary to resort to a high degree of amplification, as high as tive stages of amplilication. being required. This high amplification results in distortions that are objectionable.'

Where the radio program is staged at a auditorium, other than the studio forming part of the radio station, it is necessary to employ thev telephone lines for making the necessary connections. With the present microphone transmitters, it is necessary to intcrpose an amplifier between the transmitter and the telephone line in order to transmit the sound waves to the apparatus'of the station. 'lhis makes it 'necessary to transport to the auditorium anamplifer, as well as the transmitter microphone.

It is the object of lthis invention to produce a. transmitter that can be successfully employed in connection with all sound Waves within the range of audibility; which can be successfully' operated in parallel and which can be connected directly to the telephone lines.

Our improved ktransmitter briefly described consists of a stretched steel diphragm of substantially one-thousandth part of an inch in thickness, adjacent toone side of which we support the ends of soft iron ezt-4 tensions which are secured to the poles of a permanent magnet. Each of the soft iron extensions have a coil of iine msulated Wire, which coils are connected 1n series. lVhen `the diaphragm ovibrates, there will be a change in the magnetic flux passing through the coils and this will set up an electromotive force whose value varies in accordance with the frequency and amplitude of the vibrations of the diaphragm. Whenthe terminals of the magnet coils are connected to the terminals of a suitable amplifying device, currents corresponding in frequency `and intensity with the sound vibrations will be produced.

In order more clearly to describe theinrvvention and to explain its operation, reference Will now be had to the accompanying drawing in which the preferred embodiment thereof has been illustrated and in which:

Fig. l is a side elevation of the improved transmitter, a portion of the enclosing casing being broken away `to show the method of suspension; i

Fig. 2 is a section taken on line 2 2, Fig. l;

Fig. 3 is a section similar to that of Fig. 2 showing the parts to a larger scale;

F ig. 4 is a section taken on line 1 -4, Fig. 3, and illustrates a detailof the construction; Fig. 5 is a section taken on line/5v5, Fig. 2; and

Fig. 6 is a section similar .to sectionB and shows a slightly modified form of construction.

The numeralv 1 indicates the usual casing in which the transmitter is. enclosed. This case has a base 2 and is provided with a plurality of screened openings 3.

The transmitter has been indicated as a whole by numeral 4 and is suspended within the casing by means of a plurality of' coiled springs 5, which extend between eyelets 6 and 7 which are respectively secured to the transmitter 4 and the casing 1. Q

The transmitter consists of a metal ring 8, preferablyuof circular' shape and has a central opening whose wall is threadedl 1n the manner indicated by numeral 9. ring 10 has its outer surface threaded and 1n cngagement with the threads 9. A second Vring 11, of the same diamter as ring 8, but of less thickness,

is secured to the latter by A diaphragm 13, which sheet of'steelpf means of screws 12. is formed from a circular i a thickness of about one one-thousandth of an inch, has its outer edges clamped between rings 8 and 11, so as to beheld firmly. The outer edge of the diaphragm is commonly corrugated so that it will offer greater resistance against movement, but this has not beenshown as it is old. A. separator ring 14 is placed between the ring 10 and the diaphragm 13 and has the side next to the 'diaphragm rounded. By turning ring 10,

the ring 14 will be forced against the diaphragm and distortthe same in the manner shown in Fig. 3. Tn this manner and by this means the diaphragm is stretched so that it will respond to the highest frequency sound waves that are used in music, either' vocal or instrumental. Tn order to translate the vibrations of the diaphragm intp a corresponding. variable electric current, we have provided a permanent magnet 15 to the poles of which we have secured soft iron cores`16, each of 'which is provided with a' coil 17. The electromagnet --is placed in a casing having a bottom 18 and circular side wall 19. The magnet 15 is placed against the inner surface of the bottom 18\and is held in position by an insulating filling, 20, which may be sealing wax, bakelite or any other suitableinsulating material that can be poured about the magnet and which will harden in place, The surface of the filling is now gr^und so as to make it a plane. The

edge of the side wallv 19 and the ends of the magnet cores are also ground so that they iwill lie in the same plane. The outside diameter of the casing is slightly smaller than the opening in the ring 11, so that it can be inserted into the latter. A paper ring 21 of a `thickness of about one one-thousandth' '0 an inch is placed between the diaphragm 13 and the edge of wall 19 and serves to space the surface of the wax andthe ends of the pole extensions 16 from the dia-,

phragm.' A ring 22 frests o n the outside of the bottom 18 and ,is provided with openings for the reception .of clamping screws 23,

meeste which serve to hold the magnet casing in place. The ends of coils 17 are connected to the insulated binding posts 24 from which conductors 25 extend to an ampliiier, which has not been shown, a condenser 26 is connected between the binding post 24 (Fig. 2).

Tn Fig. 5, we have shown how ring 22 and the screws 23 may be dispensed with. This can be done by threading the opening in ring 11 and threading the wall 19 to correspond. |The casing is then screwedinto ring 11.

Tn Fig. 2 we have shown the diaphragm thickened at 27. This is for the purpose of providing a magnetic path of greater magnetic conductivity than could be had from the diaphragm alone. This thickening is attained by securing to the steel diaphragm a disk of soft iron.

When the ring 10 is rotated, it has a tendency to rotate ring 14 and to prevent this, ring 14 is provided with a pin` 28, which engages an opening in part 8.A This is` merely illustrative or' a means for this purpose and any other suitable means may be employed if desired.

lLet us now suppose that the wires 25 are connected to some suitable amplifying device and that the diaphragm 13 is subjected to sound vibrations. The diaphragm 13 will vibrate towards and away from the ends of the magnet poles 1G. This will vary the reluctance of the magnetic path and consequently the number of lines of force that pass through coils 17.` The variations in 'the magnetic flux within coils 17 sets up an electromotive torce which is transmitted by wires. 25 to the ampliiier. Since the diaphragm is thin and taut, it will vibrate freely when subjected to sound vibrations and will set up corresponding electrical impulses in the coils 17 and wires 25. its soon as the diaphragm is removed, from the iniuence of' the sound waves, the magnetic lines of torce will set up eddy currents in the diaphragm when the latter vibrates and these will exert a retarding action which will function to stop the vibrations ont the diaphragm. 5

Let us now suppose a case in which several transmitters are yconnected in parallel as for the broadcasting of an opera or a rplay. The diaphragm nearest the source or the sound 'will vibratel with the greatest intenwlres 25 ma extend to the studio, whereas with mlcrop ones now in use, th1s cannot be done.

A hole 29 (Fig. 3) extends through the bottom 18 of the casing and through the insulating material 20. This permits air to be displaced during the vibrations of the diaphragm.

The Water proof insulating material 20 which has been shown as surrounding the electromagnets and coil 17, in addition to its function in holding the electromagnet in place, also performs another very important function, namely this, that it prevents the pole pieces 16 from vibrating and setting up sound vibrations which would interfere with the proper transmission. I have found from experience that if themagnet is securedto the casing by screws alone, or by any other clamping means, that they Will vibrate and thereby deleteriously effect the operation of;

the transmitter. Vhen they are embedded, as shown, in Wax, shellac, bakelite or any other nonmagnetic material, this vibration is prevented and better results are obtained. The filling 20 also performs .the function of providing an air chamber which is in com. manic-ation with the atmosphere through the opening 29.' This produces a dampening action, which prevents the diaphragm from vibrating except when subject to sound impulses. 1 y

On account of the fact that all the electrical conducting parts are thoroughly insulated and that the action of the transmitter great benefit as the operation will e constant under all conditions of humidity and the transmitter can also be used for submarine detection andv other Work Where it is required to be immersed in liquid.

Having described the invention what is claimed as new is:

A transmitter for radio broadcasting comprising, in combination, a ring having its inner surface threaded, a clamping ring of substantially the same size as the iirst mentioned ring, a diaphragm having its outer edge located between the rings, means for forcing the rings towards each other so as to clamp Athe diaphragm, a third ring having its outer surface threaded and in cooperative engagement with the threaded surface ofthe first mentioned ring, a separator ring between the last mentioned-ring and the (iliaphragm and means for preventing the separator ring' from rotating with respect to the diaphragm whereby the latter will not be subjected 'to friction when the third ring is rotated.

In testimony whereof we affix our signatures.

HARRY A. MILLS. WILLIAM D. PYLE. 

